Storage apparatus having a recording medium with a thermal insulation barrier

ABSTRACT

A method for fabricating a patterned recording medium includes providing a workpiece with a non-magnetic substrate and at least one overlying magnetic layer, laminating a thermal insulation barrier partially in a soft under layer of one of the at least one magnetic layers and forming a topographical pattern including a plurality of trenches in the soft under layer. Blocks of track triplets are formed between adjacent trenches that are magnetically and thermally insulated from other adjacent blocks of track triplets.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

Embodiments of the present invention relate to U.S. ProvisionalApplication Ser. No. 60/747,060, filed May, 11, 2006, entitled the same,the contents of which are incorporated by reference herein and which isa basis for a claim of priority.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate generally to heat assistedmagnetic recording. In particular, embodiments of the present inventionrelate to a method and apparatus for heat assisted magnetic recordingusing a patterned recording medium and a method of manufacturing apatterned recording medium used in heat assisted magnetic recording.

2. Related Art

Heat assisted magnetic recording (HAMR) generally refers to the conceptof locally heating a recording medium to reduce the coercivity of therecording medium so that an applied magnetic field can more easilydirect the magnetization of the recording medium during the temporarymagnetic softening of the recording medium caused by the heat source.HAMR has been proposed as a means by which the recording density of harddisc drives may be extended to 1 Tb/in² or higher. Current conventionalhard disc drive technology is limited by the superparamagnetic limit,which causes the small magnetic grains needed for high density recordingmedia to gradually lose their magnetization state over time due tothermal fluctuations. By using HAMR, the magnetic anisotropy of therecording medium, (i.e., its resistance to thermal demagnetization), canbe greatly increased while still allowing the data to be recorded withstandard recording fields. For example, a laser beam, acting as a heatsource, heats an area on the recording medium (called an “optical hotspot”) that is to be recorded and temporarily reduces the anisotropy injust that area sufficiently so that the applied recording field is ableto set the magnetic state of that area. After cooling back to theambient temperature, the anisotropy returns to its high value andstabilizes the magnetic state of the recorded mark.

The main difficulty with HAMR has been discovering a technique that isable to conduct sufficient light energy into the recording medium toheat it by several hundred degrees, but only in the area that is desiredto be recorded, which typically will have dimensions on the order of 25to 50 nm if the recording density is 1 Tb/in². If the optical hot spotis larger than this area, it will extend to neighboring bits and trackson the recording medium, and by heating those areas as well, the datarecorded in those areas will be erased. Confining the optical hot spotto an area that is much smaller than a wavelength of light, and wellbelow a so-called “diffraction limit” that can be achieved by standardfocusing lenses, is an area of study called “near field optics” or “nearfield microscopy.” Conventional techniques have been described forconfining light to 20 nm spots or smaller. However, these techniqueshave not demonstrated a capability for delivering a substantial amountof optical power to the sample within that small spot.

Several drawbacks exist with the near field optics technique ofconfining the optical hot spot. In general, a near field optics systemgenerates high thermal gradients that define a written bit in both thedown track and cross track directions in the presence of a low gradientfield that flips the magnetization within the optical hot spot. Thethermal conductivity of the recording medium is high so as to generatehigh thermal gradients but this requires higher power from the laser.Thus, one drawback with the near field optical technique is therequirement of a device or method to concentrate the laser beam in thedesired spot efficiently.

Another drawback with the near field optical technique is exposing onlyone track of the recording medium at a time to the optical hot spot,which causes the spot to be very small. This requires greaterconcentration of the laser beam resulting in reduced efficiency (i.e.,the power in the recording medium divided by the total laser power).When the size of the optical hot spot is much less than the wavelengthof the light, it is very difficult to obtain acceptable efficiencybecause most of the light reflects off the aperture even with cleverlydesigned electron plasma resonance structures. For example, a 1 Tb/Sqsystem with a bit aspect ratio of 4 (i.e., bpi/tpi=4) would need a spotsize of about 60 nm. This is only 13% of the wavelength of blue light.Thus, the efficiency problem is severe.

An even greater disadvantage with the near field optics technique is therequirement to co-locate the optical hot spot and the write field of theread/write head. This arrangement greatly compromises the write fieldgradient that is obtainable from the read/write head so that thetransition must be defined mainly by the thermal gradient. Also, from adesign and manufacturing perspective, it is much difficult to optimizethe magnetic field and thermal structures simultaneously in a singlestructure.

Therefore, the need arises for a HAMR system that can extend magneticrecording to higher density by thermally lowering the coercivity of therecording medium in an optical hot spot during a write operation andthus, achieve a higher coercivity recording medium with greater roomtemperature thermal stability for write operations. The need also arisesfor a HAMR system that confines the optical hot spot to a narrow regionas not to heat adjacent tracks causing adjacent track erasures for manywrite operations and mitigates the problem associated with combing themagnetic and thermal write operations in the HAMR system.

SUMMARY OF THE DISCLOSURE

Embodiments of the present invention address the problems describedabove and relate to a method and apparatus for heat assisted magneticrecording using a patterned recording medium and a method ofmanufacturing a patterned recording medium used in heat assistedmagnetic recording.

According to one embodiment of the present invention, a method forfabricating a patterned recording medium includes providing a workpiecewith a non-magnetic substrate and at least one overlying magnetic layer,laminating a thermal insulation barrier partially in a soft under layerof one of the at least one magnetic layers and forming a topographicalpattern including a plurality of trenches in the soft under layer.Blocks of track triplets are formed between adjacent trenches that aremagnetically and thermally insulated from other adjacent blocks of tracktriplets.

According to another embodiment the of present invention, a method forheat assisted magnetic recording includes generating a light beam on arecording medium having multiple track triplet structures, upstream fromwriter poles and confining the laser heat from the light beam to one ofthe track triplet structures. The method also includes rotating therecording medium such that trailing edges of the writer poles reach aheated portion of the recording medium caused by the light beam beforethe heated portion cools. The light beam and the writer poles areprovided in a non-collocated manner due to the heat retained in theheated portion.

According to a further embodiment of the present invention a storageapparatus using heat assisted magnetic recording includes a magneticrecording medium and an arm for positioning a magnetic recording headadjacent to the magnetic recording medium. The magnetic recording mediumincludes a laminated thermal insulation barrier partially in a softunder layer of one of at least one magnetic layers and a plurality oftrenches in the soft under layer, with blocks of track triplets formedbetween adjacent trenches that are magnetically and thermally insulatedfrom other adjacent blocks of track triplets. The magnetic recordinghead includes a gang of writer poles positioned above the magneticrecording medium in a non-collocated manner with respect to a lightbeam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates generally a pictorial representation of a disc drivesystem constructed in accordance to one embodiment of the presentinvention.

FIG. 2 illustrates a plan view of a heat assisted magnetic recording(HAMR) gang write system and patterned recording medium according to oneembodiment of the present invention.

FIG. 3 illustrates a down track cross sectional view of a HAMR gangsystem and patterned recording medium according to one embodiment of thepresent invention.

FIG. 4 illustrates a magnetic phononic super lattice thermal insulationbarrier fabricated recording medium according to one embodiment of thepresent invention.

FIG. 5 illustrates a graph of the thermal resistance of a sputteredAl₂O₃ verses the thickness of the gap layer.

FIG. 6 is a flowchart depicting steps performed in fabricating apatterned recording medium according to one embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A method and apparatus for heat assisted magnetic recording using apatterned recording medium and a method of manufacturing a patternedrecording medium used in heat assisted magnetic recording is disclosed.In the following description, numerous details are set forth. It will beappreciated, however, to one skilled in the art, that embodiments of thepresent invention may be practiced without these specific details. Inother instances, well-known structures and devices are shown in blockdiagram form, rather than in detail.

An explanation will be given below regarding embodiments of the presentinvention while referring to the attached drawings. Embodiments of thepresent invention encompass structures that can be used in recordingheads for use with magnetic and/or optical recording medium, as well asmagnetic and/or optical recording heads that include such devices anddisc drives that include the recording heads. FIG. 1 is a pictorialrepresentation of a disc drive 10 constructed in accordance withembodiments of the present invention. The disc drive includes a housing12 (with the upper portion removed and the lower portion visible in thisview) sized and configured to contain the various components of the discdrive. The disc drive includes a spindle motor 14 for rotating at leastone data storage medium (e.g., a disc) 16 within the housing, in thiscase a magnetic disc. At least one arm 18 is contained within thehousing 12, with each arm 18 having a first end 20 with a recording andreading head or slider 22, and a second end 24 pivotally mounted on ashaft by a bearing 26. An actuator motor 28 is located at the arm'ssecond end 24, for pivoting the arm 18 to position the head 22 over adesired sector of the disc 16. The actuator motor 28 is regulated by acontroller that is not shown in this view and is well-known in the art.

FIG. 2 illustrates a plan view of a heat assisted magnetic recording(HAMR) gang write system and patterned recording medium according to oneembodiment of the present invention. The HAMR gang write system which ispart of the head 22, is represented by right outer writer pole tip 31,left outer writer pole tip 32 and central writer pole tip 30. The leftand right outer writer pole tips 31 and 32 are provided with bevelededges for skew. An optical hot spot 33 (also referred to through thespecification as a laser spot), is provided upstream of the HAMR gangwrite system. The patterned recording medium which forms part of thedisc 16, is formed into blocks of track triplets including left adjacenttrack triplet 35, right adjacent track triplet 36 and center tracktriplet 39. Adjacent trenches, left trench 37 and right trench 38 areprovided between the track triplets. Left adjacent track triplet 35,right adjacent track triplet 36 and center track triplet 39 aremagnetically and thermally isolated from other adjacent blocks of tracktriplets on the disc 16. Left and right adjacent trenches 37 and 38,respectively, provide lateral thermal isolation. This helps lengthen thecooling time constant and prevents heating of the left and rightadjacent track triplets 35 and 36, respectively.

Referring now to FIG. 3, which illustrates a down track cross sectionalview of the HAMR gang system and patterned recording medium according toone embodiment of the present invention, thermal insulation barrier 50is provided in a partly patterned soft under layer 48 which is below arecording layer 46. A carbon coating 45 is provided above the recordinglayer 46. To be more precise, thermal insulation barrier 50 is providedbetween interlayer 44 and a synthetic antiferromagnetic layer 47 whichis part of the soft under layer 48. All of these layer rest abovesubstrate 49. Although left adjacent track triplet 35 illustrates thevarious layers of the disc 16 discussed thus far, the right adjacenttrack triplet 36 and the center track triplet 39 also include theselayers and the discussion applies to these tracks as well. The thermalinsulation barrier 50 is a laminated structure as discussed in greaterdetail below, and has perpendicular anisotropy. As clearly illustratedin FIG. 3, left and right adjacent trenches 37 and 38, extend down toand in a most preferable embodiment of the present invention, extendthrough the thermal insulation barrier 50 such that the block of tracktriplets, 35, 46, and 39, fit between left adjacent trench 37 and rightadjacent trench 38. Left yoke 40 provides the left writer pole tip 31,right yoke 41 provides the right writer pole tip 32 and center yoke 42provides the center writer pole tip 30.

According to an alternative embodiment of the present invention, disc 16could have an unpatterned structure (i.e., no circumferentiallypatterned trenches). This unpatterned structure would not any way affectthe operation and scope of the present invention.

Referring back to FIG. 2, the laser spot 33 preheats the center track 39of the disc 16 just upstream of the ganged writer pole tips 30-32. Thethermal insulation barrier 50 increases the cooling time constant sothat the heated portion of the disc 16 does not excessively cool by thetime that it has reached the writing region at the trailing edges of thewriter pole tips 30-32 due to the rotation of the disc 16. As statedpreviously, the left adjacent track triplet 35, the right adjacent tracktriplet 36 and the center track triplet 39 are magnetically andthermally isolated from other adjacent blocks of track triplets on thedisc 16 and the left and right adjacent trenches 37 and 38,respectively, provide lateral thermal isolation which helps lengthen thecooling time constant and prevents heating of the left and rightadjacent track triplets 35 and 36. Thus, the combination of the thermalinsulation barrier 50 and the left and right adjacent trenches 37 and38, significantly lengthens the cooling time constant.

As illustrated in FIG. 2, the laser beam spot 33 is allowed to impingeon the disc 16 upstream of the writer pole tips 30-32 because the heatis retained locally for an extended amount of time. Therefore, the laserbeam spot 33 and the writer pole tips 30-32 need not be exactlycollocated as discussed in the conventional HAMR systems. With thisarrangement of the laser beam spot 33 and the writer pole tips 30-32,thermal contours 34 are allowed to develop a relatively straight (acrossthe track width) shape by the time the outer writer pole tips 31 and 32are reached, so that their transitions do not get an excessive thermallyinduced skew due to rounded thermal contours.

According to one embodiment of the present invention as illustrated inFIG. 4, the thermal insulation barrier 50 is formed with alternatinglayers of amorphous SiO_(x) and a magnetically soft amorphous alloy ofcobalt-zirconium-tantalum (CZT) in order to achieve a low thermalconductivity. The SiO_(x) layers are low sonic impedance refectionlayers that provide reflectivity for a range of phonon energies and forboth pressure and shear phonons which have different velocities andimpedances. The CZT layers are magnetic metal layers that providemagnetic conductance through the thermal insulation barrier 50.

The thickness of the layers are varied so as to provide reflection of arange of phonon, which are energy quantized sonic waves that are thetransmitters of lattice heat. As illustrated in FIG. 4 and for examplepurposes only, the SiO_(x) layers 61, 63, 65 and 67 have a thicknessthat vary from 1 to 3 nm while the CZT layers 60, 62, 64, 66 and 68 havea thickness that vary from 5 to 15 nm. With the structure, the thermalinsulation barrier 50 forms a super lattice type structure yielding anengineering reflecting coating. Mixing up the thicknesses of the layersprevents selective transmission of particular phonon wavelength. Thesonic impedance Z_(sonic) is approximately equal to theSqrt[(Density*Elastic Modulus)]. The preponderance of a magnetic alloywould maintain low magnetic impedance or good magnetic performance froma soft under layer discussed in greater detail below. This magneticphononic super lattice structure for the thermal insulation barrier 50provides good magnetic conductance and thermal impedance.

According to an alternative embodiment of the present invention, thethermal insulation barrier 50 may be formed with alternating layers ofamorphous SiO_(x) and films of tungsten selenide (WSe₂) grown fromalternating layers pf W and Se layers in an ordered or disordered manneras taught in C. Chiritescu et al., “Ultra Thermal Conductivity inDisordered, Layered WSe₂ Crystals,” Science, Vol. 315, 2007, pp. 351-353and K. Goodson, “Ordering Up the Minimum Thermal Conductivity ofSolids,” Science, Vol. 315, 2007, pp. 342-343. The contents of thesearticles are incorporated herein by reference.

FIG. 6 is a flowchart depicting steps performed in fabricating apatterned recording medium according to an embodiment of the presentinvention. The process begins from a start state S100 and proceeds toprocess step S101. In the first process step according to the presentinvention, a workpiece is provided in the form of a thin-film magneticrecording medium comprising a non-magnetic substrate with at least oneoverlying magnetic layer. Additional layers intermediate the magneticlayer and substrate 2, e.g., seed layers, underlayers, intermediatelayers, etc., can be provided. Further, according to the invention, thenature (i.e., type) of magnetic medium is not critical for practice ofthe invention, and therefore the at least one magnetic layer may beappropriately structured, for example, for longitudinal, perpendicular,laminated, anti-ferromagnetically coupled (AFC), and granular media.

In a second process step S102, according to the present invention, alaminated thermal insulation barrier is formed partially in the softunder layer of one of the magnetic layers. This laminated thermalinsulation barrier is formed with alternating low sonic impedancereflection layers and magnetic metal layers. The thicknesses of thelayers vary as discussed in greater detail above in FIG. 4.

In a third process step S103, an overlying protective overcoat layer isadded. The protective overcoat layer may be formed of any hard, abrasionresistant material suitable for use in hard disk applications, e.g., adiamond-like carbon material.

In a fourth process step S104, according to the present invention, theprotective coating layer is subjected to patterning for forming atopographical pattern therein, corresponding to the type of patternedmedia desired to be formed. As illustrated in FIG. 3, the topographicalpattern includes a plurality of elevated areas and recessed areas calledtrenches of appropriate dimensions and spacings for defining the desiredpattern in one of the magnetic layers called a soft under layer.According the present invention, the topographical pattern includesblocks of track triplets that are magnetically and thermally insulatedfrom other adjacent blocks of track triplets. This patterning operationproduces an interlayer provided above the thermal insulation barrierwhich above a synthetic antiferromagnetic layer. The protective coatinglayer may be topographically patterned via conventionalphotolithographic techniques.

The process terminates at state S105.

Various alternative embodiments of the present invention are providedbelow. According to one alternative embodiment of the present invention,the soft under layer 48 could be provided with trenches that separateindividual tracks which would help isolate the track triplets from eachother magnetically and enhance the write field. According to thisalternative embodiment, three times better lithography would be requiredto produce the disc 16. Also the top region of the soft under layer 48,is narrowed by more than three times which makes the syntheticantiferromagnetic magnetization pattern of the syntheticantiferromagnetic layer 44, harder to achieve (i.e., it would requirehigh anisotropy field in the CZT). The synthetic antiferromagneticmagnetization pattern is important for smooth (low jitter) writing.

Another alternative embodiment of the present invention includes a lowthermal conductivity layer based on organic polymers or other materialsrather than laminants of SiO_(x) and CZT for the thermal insulationbarrier 50. In addition, the disc cooling time could be enhanced byincluding high heat capacity and high thermal conductivity (in thecircumferential direction) layers above and/or as part of the thermalinsulation barrier 50. Therefore, magnetic alloys with high thermalconductivity can be used for the part of the synthetic antiferromagneticlayer 44. An alloy of CO₉₀Fe₁₀ is expected to have a thermalconductivity that is ten times better than CZT. Ifmagnetostriction/stress issue causes the synthetic antiferromagneticlayer 44 to not orient radially then an alloy of Ni₈₁Fe₁₉ is preferablebecause of its negative magnetostriction (CoFe is positive) even thoughits thermal conductivity is only five times better than CZT. Finally alayer of very high thermal conductivity material (e.g., Cu, Ag, diamondlike carbon) can be provided between the synthetic antiferromagneticlayer 44 and the thermal insulation barrier 50 to further enhance thecooling time constant.

High thermal conductivity in the down track direction can lengthen theeffective cooling time a low velocities and thus allow greater laserbeam spot to zone separation. Thus, according to a further alternativeembodiment of the present invention, using high thermal conductivitymaterials such as CoFe, for example, for the synthetic antiferromagneticlayer 44, instead of CZT as illustrated in FIG. 3, benefits low velocityapplications. According to a further alternative embodiment of thepresent invention, a high thermal conductivity material such as copperor silver, for example, can be placed between the thermal insulationbarrier 50 and the synthetic antiferromagnetic layer 44 to lengthen theeffective cooling time.

According to embodiments of the present invention, a thermal insulationbarrier coupled with track patterning in the form of block of tracktriplets, confines the laser heat from a laser to the track that isbeing written. This allows the laser beam spot to impinge on the discupstream of the writer pole(s) because the heat is retained locally foran extended amount of time. Therefore, the heat source (i.e., the laserbeam spot) and the writer poles need not be exactly collocated. Thus,this mitigates one of the disadvantages of the conventional HAMRsystems. With this arrangement of the laser beam spot and the writerpoles, thermal contours are allowed to develop a relatively straightshape by the time the outer writer poles are reached, so that theirtransitions do not get an excessive thermally induced skew due torounded thermal contours.

In addition, in order to achieve thermal insulation to the adjacenttracks, the trench provided in the soft under layer also providesreduction in fringe field to the neighboring tracks and boost the wirefield of the narrow outer pole tips. Thus, the arrangement of thethermal insulation barrier coupled with the track patterning trenchespartly through the thermal insulation barrier and a syntheticantiferromagnetic layer, minimize the affects of adjacent track erasurefrom thermal spreading, minimizes laser power requirements, straightensthe thermal contours for higher readable liner bit density, and allows alarger distance between the laser beam spot and the writer pole tipswhich makes designing more feasible. The thermal insulation barrier isformed of laminated magnetic and ceramic layers for high thermalimpedance in the normal direction and low magnetic impedance. Thethermal insulation barrier has high thermal conductivity layers in thecircumferential direction for lengthening effective cooling time andhigh thermal capacity layers (all the metal layers plus potential foradditional dead layers) above or as part of the thermal insulationbarrier.

The following provides an example of manufacturing a magnetic phononicsuper lattice thermal insulation barrier for a recording mediumaccording to the present invention. In the example, SiO_(x) is replacedwith Al₂O₃ and the findings of FIG. 5 are referenced in the example.

EXAMPLE

Approximate calculations (assumes very high media velocity and lowthermal conductivity in the circumferential direction), of the thermaltime constant (in the case of high media velocity) predict that thecooling time constant, τ (i.e., T=To exp(−t/τ)), for a laminant of 4×[1to 3 nm thick Al₂O₃ and 10 nm thick CZT] under a total thickness of 50nm of metals (top synthetic antiferromagnetic soft under layer,interlayer and data layer), will be about 25 ns if lateral thermalconductance is prevents by DTR trenches. This calculation multiplies by4 the thermal resistance (i.e. R_(B)=2.8×10⁻⁸ m² K/W) for a very thinAl₂O₃ between a gold heater and a silicon thermal ground layer that wasmeasured and illustrated in FIG. 5, assuming that the phononreflectivity from CZT interfaces is similar to that of gold and silicon.This was shown to be better so this is a worse case assumption). Thiscalculated time constant is just the product of the heat capacity perunit area (i.e., C=(heat capacity/area)=(metal heat capacity/volume=3.2MJ/K.° m³)*(average thickness=50 nm+0.5*(40 nm of CZT)=70 nm)=0.224J/K.° m²) of the metals (above the thermal insulation barrier and halfway into it) times the thermal resistance through the thermal insulationbarrier (i.e., R=4R_(B)=1.12×10⁻⁷ sm² K.°/J). That isτ=RC=0.224*1.12×10⁻⁷=25 ns.

The variability in Al₂O₃ layer thicknesses (i.e., 2 to 4 nm) proposedhere allows each layer to maximize its phonon reflectivity for differentphonon energy ranges. This calculation assumes an Al₂O₃ ceramic becausedata is available for it. The preferred embodiment using amorphousSiO_(x) layers is expected to have even larger thermal impedance (˜x2larger), longer cooling times, and less temperature drop between thelaser spot and the most down stream outer writer pole tip.

If the down stream edge of the outer writer poles is 0.4μ down stream ofthe laser spot edge and the media velocity is 40 m/s, then the transittime is 10 ns. Therefore the data layer will cool by only 33% (i.e.,1-exp (−10/25)=0.33) by the time it has passed the most remote outerpole tips. The media under the pole surface where old data isoverwritten will be even hotter thus enhancing the overwrite process. Inaddition, the thermal gradient will combine (weakly) with the writefield gradient to yield sharper transitions.

Calculations predict that the required absorbed power for the aboveconditions with a 500 ktpi system (i.e., 6μ″ per track triplet) is only0.4 mW for heating up to 320° C. at a media velocity of 40 m/s. This isa very feasible amount of power in that it allows for low transferefficiency through the near field optics.

The increase in effective cooling time, τ, provided by high heatcapacity and high circumferential thermal conductivity is quantified bythe following equation:τ=(2C _(c) /kv ²)/(−1+Sqrt[1+4C _(c)/(Rdk ² v ²)])  (1)where: v is the media velocity (m/s); C_(c) is the circumferentialthermal conductance average over the thickness of all of the layersabove the thermal insulation barrier (e.g., Co₉₀Fe₁₀ has C_(c)˜400J/smK.°); k is the average heat capacity (e.g., k=3.2×10⁶ J/K.° m³ fortypical metals which are nearly equal for most metals) of the metallayers above the thermal insulation barrier; d is the total thickness(e.g., d=7×10⁻⁸ m) of the layers; and R is the thermal impedance of thethermal insulation barrier (e.g., R=1.12×10⁻⁷ sm² K.°/J for a 4 layeralumina [more for SiO_(x)] based magnetic phononic super lattice typethermal insulation barrier).

For high velocity (defined by 4 C_(c)/(Rdk² v²)<<1) Eq 1 reduces to:τ˜Rkd=25 ns for the above parameters as before  (2)

However the approximation that 4 C_(c)/(Rdk² v²)<<1 is not even achievedfor a CZT synthetic antiferromagnetic soft under layer above the thermalinsulation barrier let alone for a CoFe based one. When the aboveassumed values for the parameters (CoFe synthetic antiferromagnetic softunder layer) in Equation 1 are assumed the calculated effective timeconstant is τ=59 ns even at v=40 m/s. Therefore, the temperaturereduction from the maximum at the outer write zones (0.4μ down stream)is only 16%.

For a CZT based synthetic antiferromagnetic soft under layer, thecircumferential thermal conductance is 10 times worse (i.e., C_(c)=40J/s mK.°) worse so the resulting effective cooling time is τ=31 ns. Thisis almost half of that for a CoFe synthetic antiferromagnetic soft underlayer. The resulting reduction in temperature at the outer writer polesis then 28%. The difference between these numbers and the approximateones (i.e., τ˜25 ns and temperature loss=33%) is due to the fact that 4C_(c)/(Rdk²v²) ˜1 and not <<1 for a CZT synthetic antiferromagnetic softunder layer. So the temperature loss for CZT is almost twice that ofCoFe.

The thermal time constant, τ, calculated by Equation 1 above gives therate of exponential decay of the temperature at a point in the movingmedia. Correspondingly, at an instant in time the temperature decaysexponentially with a decay length of Δ as one moves away from the laserspot. Of course the relation between these constants is:Δ=V_(τ)  (3)And the temperature verses time and position in the rest frame of themedia, X_(m), is given by:T=T _(max)exp(−t/Σ−X _(m)/Δ)  (4)

The position in the rest frame of the head is just:X _(h) =X _(m) −vt  (5)So in the rest frame of the head, with the laser spot trailing edge atX_(h)=O, the thermal profile at all times is given by:T=T _(max)exp(−x _(h)/Δ)=T _(max)exp(−x _(h) /Vτ)  (4)And the fractional temperature loss verses distance from the laser spotedge is:Loss Fraction=1−T/T _(max)=1−exp(−x _(h) /V _(τ))  (5)

Of course it may be desirable to minimize this loss to: reduce adjacenttrack erasure; and to minimize the maximum temperature in the media toprevent reliability problems associated with lube loss (and depositionon the optics) and materials degradation in the head and media; and tominimize the required laser power.

Calculations for the magnetic phononic super lattice structure for thethermal insulation barrier are as follows. The compression wave sonicvelocity in a media is:Vs=sqrt(Y/τ)  (6)where Y is the elastic modulus and Γ is the density. The sonic impedanceis analogous to the impedance of a transmission line and is:Z=sqrt(Yρ)  (7)The reflection coefficient at the junction with a dissimilar materialwith impedances Z and z is:R=(Z−z)/(Z+z)  (8)

The fraction of incident power reflected is R². Negative R correspondsto a 180° phase shift in the reflected wave.

It may be desirable to maximize the absolute value of R for a range onphonon energies, E, near the average thermal excitation energy for threedegrees of freedom (i.e., E=3 kT/2=6×10⁻²¹ where k is Boltzman'sconstant and T is degrees Kelvin). The frequency, f, of the phonons isf=h/E=9 THz (i.e., h=Plank's constant=6.6×10⁻³⁴ J). For metals such asiron the compression wave sonic velocity, v, if about 6000 m/s so thewavelength of the average phonon is λ=v/f=7 Angstroms. For shear wavesthe velocity is about half so the wavelength is about 3.5 Angstroms. Foramorphous SiO_(x) the velocities are expected to be about half again sothe corresponding wavelengths are reduced by another factor of two.Therefore, SiO_(x) layers of the order of 1 nm thick will contain manywavelengths and constructive interference (from the two surfaces) of thephonons propagating through the layer will be minimized. That is thatthe SiO_(x) will not act like an antireflection coating for averagephonons. By using a range of layer thickness (i.e., 1 to 3 nm) and thickCZT layers, constructive interference and transparency to particularphonon energies and incident angles is avoided. This is the essence ofthe magnetic phononic super lattice approach to a thermal insulationbarrier.

If we use a single layer of low Z low thermal conductivity material suchas the commonly used photosensitive organic material known aspolymethylmethacrylate (PMMA) the thermal resistivity will be enhancedby the phonon surface scattering so it will get a contribution ofmagnitude R_(B)=2.8×10⁻⁸ sm² K.°/J similar to the result of shown inFIG. 5. In order to quadruple the thermal resistance from this value(i.e., the resistance used in the conceptual magnetic phononic superlattice design discussed here) the thickness of the PMMA would have tobe about 20 nm thick (i.e., d=RC=3 R_(B)C=20 mm for C˜0.25 J/smK.°).This would be a significant increase in magnetic impedance (i.e., ˜x2)over the proposed magnetic phononic super lattice and it would incur thefragility penalty discussed above. However a material research effortmight uncover a low thermal conductivity material that would be suitablefor this application and thus avoid the need for the magnetic phononicsuper lattice enhancement of the present invention.

The embodiments disclosed herein are to be considered in all respects asillustrative, and not restrictive of the invention. The presentinvention is in no way limited to the embodiments described above.Various modifications and changes may be made to the embodiments withoutdeparting from the spirit and scope of the invention. The scope of theinvention is indicated by the attached claims, rather than theembodiments. Various modifications and changes that come within themeaning and range of equivalency of the claims are intended to be withinthe scope of the invention.

1. A storage apparatus using heat assisted magnetic recording,comprising: a magnetic recording medium; and an arm for positioning amagnetic recording head adjacent to the magnetic recording medium,wherein the magnetic recording medium includes a laminated thermalinsulation barrier partially in a soft under layer of one of at leastone magnetic layers and a plurality of trenches in the soft under layer,with blocks of track triplets formed between adjacent trenches that aremagnetically and thermally insulated from other adjacent blocks of tracktriplets, wherein the magnetic recording head includes a gang of writerpoles positioned above the magnetic recording medium in a non-collocatedmanner with respect to a light beam.
 2. The storage apparatus using heatassisted magnetic recording according to claim 1, wherein a syntheticantiferromagnetic layer, in the soft under layer, is provided above thethermal insulation barrier.
 3. The storage apparatus using heat assistedmagnetic recording according to claim 2, further comprising a thermalconductive material between the synthetic antiferromagnetic layer andthe laminated thermal insulation barrier.
 4. The storage apparatus usingheat assisted magnetic recording according to claim 1, wherein thelaminated thermal insulation barrier includes alternating low sonicimpedance reflection layers and magnetic metal layers.
 5. The storageapparatus using heat-assisted magnetic recording according to claim 4,wherein the low sonic impedance reflection layers are amorphous SiO_(x)and magnetic metal layers are cobalt-zirconium-tantalum.
 6. The storageapparatus using heat assisted magnetic recording according to claim 1,wherein the thermal insulation barrier is formed with tungsten selenide.